Re: A case for the eradication of unmanned Mars missions

"Robert J. Bradbury" wrote:
> > On Wed, 8 Dec 1999, Brian D Williams wrote:> > The notion of "Cheap Power from space" has been thoroughly> > discredited, see Robert Zubrins "Entering Space" for details.> >> > I strongly doubt that Zubrin understands either self-replication> or nanotechnology sufficiently to *discredit* "Cheap Power from> Space". All he can possibly do is point out that using current> technologies it isn't going to be "cheap".

Entirely true, especially since *peak* power can be sold to the utilities
at higher prices- simple earthbased photovoltaic without storage is very
closee to being profitable even now, while O'Neill-type space systems would
require huge risky investments with poor ROI.

> I mean really now,> quoting Zubrin as a source on this list? For heaven's sake> this man wants to *colonize* something at the bottom of a> gravity well. That means you are going to have to pay> through the nose every time you want to go someplace else> or ship something. Give me exclusivity on the Mars to Earth> FedEx route and I'll show you a rich man.

Actually, with direct entry into the Mars atmosphere, Mars is easier to get
to than the moon, in terms of delta-V. Granted, you need a larger crew
vehicle for the longer mission duration, but if it's a colonization
mission, you need the living quarters anyway. It has advantages for
near-term colonization in that volatiles can certainly be extracted from
the atmosphere. As for Mars to Earth transportation, the propulsion can be
supplied by a single stage *pressure fed* LOX-methane rocket, about the
dumbest of dumb boosters.

A dispassionate examination of the detailed trades seems not to favor
either approach. I've been a senior assoiciate of SSI *and* a Mars
Undergrounder, so I've looked at both pretty closely, and it seems a wash.

> Since you have to have a completely sealed environment anyway> (otherwise your atmosphere leaks out) you are never going to> lose any H2O. So you can get buy with a lot less than you> need in an Earth based environment. With colonization you> are going to need power, lots of it, and for that the moon> is better.

Habitats leak, and badly. Current state of the art, given the trades
between fabrication costs, mass per unit volume, etc, yield habitats with
nearly 1%/day overboard leakage. Every joint, hatch, power feedthrough,
and window mount _leaks_, and substantial amounts of makeup gases and water
will be needed.

Power is the weakness of Mars bases, volatiles *and* power (2 week nights)
are both a problem for lunar bases. An appropriate asteroid may allow good
access to sunlight for power as well as containing adequate volatiles, but
if the delta-V requiremenat are low, the launch windows are rare, a
catch-22 of the synodic period.

Without lunar volatiles, I feel Mars would be a better choice, and random
NEOs might have advantages at particular times, but at the cost of very
long manned missions.

> > >You're still dead if there's a decompression. You still leak stuff> > >outside and have to continuously replace it. But you cannot launch> > >anything with a mass driver from the surface, with the possible> > >exception of the top of Olympus Mons.> > Eugene, I don't think thats accurate. If you've got calculations> I'd like to see them. NASA is studying mass drivers to assist> launching on Earth, so I would think they have to work on Mars.> The question comes down to whether the friction limits launch> speed to sub-orbital rates, in which case you need rocket assists.

You don't need mass drivers on Mars- a skyhook lowered from Phobos can
troll through the upper atmosphere at about mach 1 (250 m/s in cold CO2),
with a good taper ratio. Indeed, Phobos & Deimos are wonderful resources
for O'Neill development in the Mars system, far better than our own moon.

> > >Mars should be a second> > >step. If you have the Moon, Mars is easy. Not vice versa. And you> > >can't do both, it's too expensive.> > If you did self-replication here on Earth first, you could do them> both very quickly and very cheaply...

Yeah, if we had some ham, we could have ham & eggs, if we had some eggs...